Food is subject to chemical and biological processes which modify its composition and can also produce substances that are detrimental to health. For example, food can oxidize, or it can be modified by enzymes and microorganisms, for example mould fungi. For food to be safely consumed by the consumer, and to be transportable and nonperishable as long as possible, these processes must be prevented or at least sufficiently delayed within the desired storage life.
One possibility is to extremely sugar, salt or dry the food to remove water from the food and to thus hinder the development of microorganisms, such as mould fungi or bacteria. The addition of alcohol or vinegar, the addition of preservatives as well as cooling slow down the development of microorganisms and reduce the activity of enzymes. Furthermore, heat treatment can make sure that microorganisms are killed and harmful enzymes inactivated. In pasteurization, the food is heated to below 100° C. for a certain period. However, the comparably resistant bacteria spores still remain germinable, and there is a risk in that important nutrients and flavors are also destroyed by the heat treatment.
Another method of extending the storage life of food is to fill the food into a gastight packaging and to evacuate the packaging before sealing it. Optionally, a protective gas or mixtures can be added to the packaging, for example nitrogen or CO2. By the displacement of air, for example oxygen, the activity of enzymes or microorganisms is also slowed down.
A method that has been hardly used at least on an industrial scale is the (ultra)high-pressure treatment of food. In this method, usually already packaged food is subjected to very high pressures of typically 400 MPa to 600 MPa for a certain period, for example some minutes. These high pressures make sure that harmful microorganisms in food are destroyed and killed. Smaller molecules, however, such as vitamins, which determine the taste and nutritional value of the food, are hardly affected by the high-pressure treatment. In meat products, the storage life can thus be extended, for example, by a factor of 6 to 10, compared to an untreated product.
Compared to heat treatment, high-pressure treatment has various advantages. For example, the taste is hardly changed, and the vitamin content in the food is sometimes more than twice as high after high-pressure treatment than after heat treatment. Moreover, some heat-sensitive products, for example seafood, cannot be heat-treated at all. Pathogenic germs, such as listeria, can be reliably killed, so that food safety is increased. Moreover, the internal structure of food can also be selectively influenced by high-pressure treatment, resulting in novel product possibilities, for example by gelling fruit preparations without heat. Finally, the technology for high-pressure treatment is already recognized in many countries as (food) safe. Moreover, high-pressure treatment permits a longer storage life of food while simultaneously no food preservatives are used. High-pressure treated food does not have to be permanently cooled, it can rather be stored at temperatures higher than 4 to 6° C. At the same time, the high sensory and nutritional values (such as the vitamin content) of the products or food are maintained.
In the high-pressure treatment of packaged food, problems with the packaging can arise due to the process conditions. For example, optically disadvantageous changes and even damages can occur. Especially packaging with a protective atmosphere cause problems due to the highly compressible gas proportion in the packaging. This is also a reason why up to now mainly vacuum packagings are employed in high-pressure treatment.
The inactivation of microorganisms as well as the structural modification of food components are described, for example, in EP 0 588 010 A1, EP 0 689 391 B1, EP 0 752 211 B1, EP 1 100 340 B1, DE 42 26 255 A1, or DE 37 34 025 C2, EP 1 112 008 B1, EP 1 201 252 B1, DE 196 49 952 A1, DE 197 38 800 A1, DE 199 39 677 A1, and DE 26 11 389 A1 describe the effects of high-pressure treatments on microbiological storage life and the safety of food. The application of high-pressure treatment especially for meat products is described in DE 198 01 031 C2, DE 196 53 677 C1, EP 0 748 592 B1, EP 0 683 986 B1, DE 101 01 958 A1, DE 10 2005 011 868 A1, or WO 2006/097248 A1.
A system for high-pressure treatment of food is moreover known from WO 2006/129180 A1. There, an autoclave with a high-pressure chamber is provided in which the food is subjected to high pressure. For building up the pressure, the autoclave must be sealed. Consequently, the system cannot be operated continuously. To increase the throughput of the system, it is typically operated in a batch mode where the products are introduced into the autoclave in groups, treated with high pressure and removed.
Another system for the high-pressure treatment of products can be taken from EP 0 687 421 A1. In this system, a high-pressure chamber and a low-pressure chamber are provided.
A high-pressure system which can treat industrially common quantities does not yet exist. Only many/several parallel autoclaves which are normally also loaded manually could master the output.